Main symptoms

Thanatephorus cucumeris ( Rhizoctonia solani ) is a soil fungus which develops preferentially on organs present in the soil or located nearby. Very polyphagous, practically present in all market garden soils, it can be found in nurseries on young seedlings as well as on adult plants. Its damage to zucchini and squash is rarely very damaging.

Like Pythium spp., It is a well-known agent damping-off on Cucurbitaceae, prevalent both pre- and post-emergence of seedlings, in particular of zucchini and squash. It produces yellowish to more or less dark brown lesions on the roots and hypocotyl. Ultimately, a canker may surround more or less the part of the stem located at the level of the soil or the substrate, causing the collapse and death of the seedling.

R. solani can also be responsible for alterations on the roots after planting:
- yellowing, browning and disappearance of small nourishing roots;
- yellowing, browning of the cortex which may become soft or superficially suberise. The lower part of the stem present in the soil can also be affected, the tissues of the cortex taking on a gray to brown green tint, and gradually rotting (Figures 1 and 2).

On or near damaged tissue, the characteristic brown mycelium of this fungus can be seen in the form of discrete, isolated filaments (Figure 3).